pnmflip --version (return code: 0)
pnmflip: Using libpbm from Netpbm Version: Netpbm 10.0
pnmflip: BSD defined
pnmflip: RGB_ENV='RGBDEF'
pnmflip: RGBENV= 'RGBDEF' (env vbl is unset)
pnmflip -h (return code: 1)
usage: pnmflip [-leftright|-lr] [-topbottom|-tb] [-transpose|-xy]
[-rotate90|-r90|-ccw] [-rotate270|r270|-cw]
[-rotate180|-r180] [pnmfile]